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-detects sound frequencies from 20 Hz to 20,000 H z.
-functions over an intensity range of 120 decibels (dB) and can discriminate
changes in intensity between 1 dB and 2 dB. -is characterized by tonotopic
(pitch) localization at all levels of the neuraxi s.
II. Outer, Middle, and Inner Ear
A. Outer ear
-consists of an auricle and an external auditory meatus. -is
separated from the middle ear by the tympanic membrane. —
conducts sound waves to the tympanic membrane, -blockage (with
wax) causes conduction deafness.
B. Middle ear (tympanic cavity)
-is located within the temporal bone.
-serves as an amplifier and impedance matching device.
-communicates with the nasopharynx via the auditory tube.
—receives its blood supply from the stylomastoid branch of the occipital or
posterior auricular artery.
-receives sensory innervation mediated by the glossopharyngeal nerve
-contains the chorda tympani of CN VII, which mediates taste sensa-
tion and parasympathetic input into the submandibular and sublingual
-pathology results in conduction deafness.
-contains the following auditory structures:
1. Tympanic membrane
-receives airborne sound vibrations and transmits energy to the mid-
dle ear ossicles.
2. Middle ear ossicles
-consist of the malleus, incus, and stapes.
178 / Neuroanatomy
—vibration of the tympanic membrane forces the footplate of the stapes
into the oval window, creating a traveling wave in the perilymph-
filled scala vestibuli.
3. Tensor tympani and stapedius muscles
-are innervated by the trigeminal and facial nerves, respectively, —
dampen vibrations of the ossicular chain, thus protecting the cochlea from
loud low-frequency sounds (< 1000 Hz ).
C. Inner ear (membranous labyrinth) [Figure 11-1] -is
derived from the otic placode of the rhombencephal on.
Thalamus Internal capsule
Transverse gyrus of temporal lobe
Auditory radiations in sublenticular part
of internal capsule
Medial geniculate body
Brachium of inf.
Commissure of inf. colliculus Inf.